Photolithography is a technique for producing images on semiconductor devices. Typically, an image formed on a mask or “reticle” is transferred to a semiconductor substrate, or wafer, where it exposes a resist layered on the substrate. It is desired to pattern smaller and smaller features on semiconductor substrates, which requires the use of shorter and shorter wavelengths of the light that is used to image the patterns. Optical lithography systems using light in the deep ultraviolet (UV) wavelengths create patterns with resolutions of about 0.25 microns. Further decreases in wavelength to 193 nm enable the imaging of patterns with resolutions of 0.18 microns and 0.13 microns. For further improvements in resolution even;shorter wavelengths are necessary, and a number of systems using the shorter wavelengths of electron beams have been proposed to image patterns with resolutions of 0.1 microns and below.
Electron beam mask projection, such as in SCALPEL, (L. R. Harriott, S. D. Berger, J. A. Liddle, G. P. Watson, and M. M. Mkrtchyan, J. Vac. Sci. Technology, B12, 3533 (1994)) use a scattering mask illuminated by electrons to pattern a substrate. While such systems are capable of high resolution, they are limited by the requirement of making multiple specialty masks, the requirement of including multiple electron lenses, and the ultimate limitation of stochastic Coulomb interactions between individual particles in the beam.
A hybrid photon-electron array printer based on a traditional deep-ultraviolet demagnification scanner-steppers and using a 4× mask is described in High throughput electron lithography with multiple aperture pixel by pixel enhancement of resolution concept, Journal of Vacuum Science and Technology B 16(6), November/December 1998, page 3177. In this proposal a 4× mask is illuminated by 106-108 optical subbeams formed by a microlens array. After demagnification these subbeams are focused on a photon-electron converter plate. Each photon subbeam triggers the emission of a narrow beam of electrons. The electron beams are focused individually on a wafer. The mask and wafer are both scanned through the many beams, exposing the entire wafer. The use of the optical imaging system simplifies the image formation and the use of the final electron patterning provides improved resolution. Further, this concept overcomes the inherent problem of Coulomb interaction present in the SCALPEL system.
Unfortunately, due to decreasing design rules and the wide use of RET (Resolution Enhancement Techniques) such as OPC (Optical Proximity Correction) and PSM (Phase Shift Masks), the masks used in image-projection systems have become increasingly difficult and expensive to make. Masks fro electron-projection systems are also extremely difficult and expensive to make. Since many masks are needed to form the multiple patterns required to manufacture an integrated circuit, the time delay in making the masks and the expense of the masks themselves is a significant cost in the manufacture of semiconductors. This is especially so in the case of smaller volume devices, where the cost of the masks cannot be amortized over a large number of devices. Thus, it is desirable to provide a fast apparatus for making semiconductor chips while eliminating the need for expensive masks. It is also desirable to improve the obtainable resolution of optical lithography. Further, such a device may be useful for directly patterning a small number of substrates, such as runs of prototype devices, and for making masks.
Accordingly, it is desirable to develop a hybrid photon-electron system having the high resolution of an electron imaging system, the simplicity and speed of optical systems, and the high throughput of a mask or massively parallel writing system, but do so without the requirement of a mask.